The long term evolution (LTE) network consists of Evolved Node B (eNB) in the evolved universal mobile telecommunication system terrestrial radio access network (E-UTRAN) and Evolved Packet Core (EPC), and the network is flat. Wherein, the E-UTRAN comprises an eNB set connecting with the EPC via the S1 interface, and eNBs are connected with each other by X2, and the abovementioned S1 and X2 are logic interfaces.
One EPC might manage one or more eNBs, and one eNB can be controlled by several EPCs, and one eNB might manage one or more cells. The long-term evolution advance (LTE-A) system is evolved from the LTE system, and the network architecture of the LTE-A is the same as that of the LTE. New technologies such as relay, spectrum aggregation and coordinated multipoint transmission/reception (CoMP) are applied to the LTE-A to improve the system performance.
With the proposal of the LTE-A, more and more attention is paid to the cell average spectrum efficiency and the cell edge spectrum efficiency by people. Comparatively, the cell edge spectrum efficiency gains most attention, this is mainly because that the LTE-A system is a frequency division system whose uplink and downlink take the orthogonal frequency division multiplexing (OFDM) or its transformation as the basic multiple access multiplexing method, which is different from the conventional wireless communication system which takes the code division multiple access (CDMA) as the basic multiple access multiplexing method, and the LTE-A system has no processing gain, and there is nearly no interference issue since it is totally orthogonal frequency division within the cell, at the cell edge, however, the interference processing is relatively tough. Since the distances from users at the cell edge to the antennas in multiple adjacent cells are little different, it is most susceptible to interference, which affects the system performance. If different antennae in multiple cells can be utilized to simultaneously provide service for the users at the cell edge, not only the inter-cell interference can be avoided, but also the multiple antennae can be fully utilized to increase spatial dimension information, so that the capacity and performance of system are significantly improved. Therefore using the transmitting antennae in multiple cells to achieve relatively high capacity and reliable transmission of wireless links at the cell edge becomes a research emphasis.
When using different antennae in multiple cells to simultaneously provide service for the users at the cell edge, since there is a coordination relationship among the multiple cells (for example, it needs to decide what kind of resources are assigned to which users at what time), meanwhile, since the antennae in multiple cells serve one or more users at the same time, this transmission method is called Coordinated Multipoint Transmission/Reception (CoMP). The CoMP can obviously implement the inter-cell interference coordination and also achieve the reliable transmission of the wireless links or increase the capacity at the cell edge.
The original purpose of introducing the CoMP is to solve the problem of inter-cell interference in the OFDM system and to increase the UE throughput at the cell edge, for example, several eNBs coordinate to remove the interchannel interference (ICI), and even to change the interference signal into the expected signal. With further research, it finds out that applying the CoMP in the LTE-A can increase the data transmission speed, cell edge throughput, and/or system throughput, thus most companies have a very optimistic view of the CoMP technology.
Coordination among multiple eNBs can increase the cell edge throughput and the average cell throughput to a very large extent, it needs, however, very high backhaul capacity for sharing data/channel state information (CSI) among multiple eNBs, and the implementation is very complicated. In order to reduce the complexity, a limited number of eNBs/cells should be considered to coordinate to serve a special UE. Therefore, a problem related to the CoMP is how to select the coordinated cell cluster (simplified as CoMP coordinated group) to maximize the cell throughput, with acceptable scheduling complexity and the backhaul capacity. At present, the existing methods can be divided into the following three kinds:
(1) Network static CoMP coordinated group;
(2) UE dynamically selects the CoMP coordinated group;
(3) Mixed-mode CoMP coordinated group.
Wherein, for the mixed-mode CoMP coordinated group, the cell set providing service for a certain UE is one subset of one relatively large fixed cluster rather than the whole network.
The handover in the coordinated multipoint environment can be divided into the following three kinds:
(1) Handover within the coordinated group: the UE belongs to the same coordinated group before/after the handover, and the same coordinated group serves the UE before/after the handover.
(2) Handover between the coordinated groups: the UE belongs to the same coordinated group before/after the handover, but a part of nodes in the original coordinated group cannot cover the UE after the handover so that they cannot serve the UE coordinately, therefore, it needs to select a new coordinated group.
(3) Handover outside the coordinated groups: the service cell after the handover does not belong to the original coordinated group, and it needs to select a new coordinated group.
As shown in FIG. 1, according to the abovementioned three kinds of handover, the UE switching from location A to location B belongs to the first kind of handover; switching from location A to location C belongs to the second kind of handover; and switching from location A to location D belongs to the third kind of handover.
The CoMP coordinated group information is very useful information for selecting a suitable target handover cell during the handover in the coordinated multipoint environment. However, the network management system can be conventionally used to configure the CoMP coordinated group information for its managed eNBs and to send the CoMP coordinated group information to the eNBs, and this method for configuring the CoMP coordinated group information lacks flexibility and cannot adjust in real time according to the network condition.